The long-term goal of the proposed experiments is the repair of damaged neocortical circuitry. The current work is focused on repair by transplantation of immature neurons. Ultimately, however, repair may also be possible by manipulation of endogenous neural precursors without transplantation. These approaches could lead to therapies for degenerative, developmental, or acquired diseases of neocortex. The effectiveness of such future therapies will depend critically on whether new neurons 1) migrate to correct locations, 2) differentiate precisely, 3) form correct long-distance projections, and 4) function within circuitry. Prior work of this grant program has focused on migration, differentiation, and connectivity. This proposal focuses on functional circuit integration. We have previously shown that transplanted immature neurons and multipotent neural precursors can selectively migrate into regions of adult mouse cortex undergoing targeted neurodegeneration of CPN, differentiate into projection-neurons, accept synaptic input, and re-form axonal projections. Experiments of the prior grant period reveal that later stage immature neurons repair circuitry with higher efficiency than earlier stage precursors. Recently, we have also manipulated endogenous precursors in situ in the adult mouse to undergo neurogenesis- the birth of new neurons- and re-formation of cortico-thalamic or cortico-spinal circuitry de novo in the adult mouse neocortex, where it does not normally occur89. This recruitment was without transplantation. A central and critical issue in the field is whether newly incorporated neurons become functionally integrated within CNS circuitry, and whether they can actually contribute to function and behavior. We have developed a range of molecular, electrophysiological, and functional sensory activation approaches to rigorously investigate to what extent the anatomic, morphologic, and synaptic integration of transplanted neurons we have previously demonstrated will be reflected in functional circuit integration, using eGFP+ donor neurons for detailed analysis of connectivity. We will also apply new approaches to enhance the cellular integration and the functional circuit formation by newly incorporated neurons. Our four specific aims will investigate whether new neurons in adult vibrissal somatosensory cortex Aim 1) acquire the precise phenotype of endogenous neurons in their cellular and temporal patterns of activation-dependent molecular signaling events;Aim 2) acquire the precise electrophysiologic phenotype to become functionally activated by sensory input;Aim 3) can be enhanced in their circuit integration by intracortical infusion of rationally selected peptide growth factors;Aim 4) can undergo enhanced functional circuit integration via enriched environmental sensory stimulation of the relevant circuitry.